Most domestic flights to Auckland Airport have now been cancelled, delayed or diverted due to fog.
More than 20 flights between Auckland and Tauranga, Palmerston North, Napier, New Plymouth, Rotorua, Nelson and the Bay of Islands have been cancelled.
Almost 30 other flights between the city and other centres, including Wellington, Christchurch, Dunedin and Queenstown, have been delayed - in many cases by more than three hours.
An Air NZ flight from Blenheim that was due in Auckland at 7.30am has been diverted to Tauranga, and a Jetstar flight from Nelson due at 7.55am has gone to Palmerston North.
The NZ Transport Agency is also warning the city's drivers to keep their headlights on and take care on the roads.
Airport operations supervisor Sam Cook said fog restrictions were put in place shortly after 6am.
"It escalated quite quickly this morning," he said.
International flights are operating as normal.
Auckland Transport has warned on Twitter that ferry services are also likely to be delayed.
A Herald reader who travelled into the CBD this morning from West Auckland said the city looked "ghostly", shrouded in a thick blanket of fog.
